1,3-Dicatbonyl compounds

Condensation of, J,iV-acetals 77 with 1,3-dicatbonyl compounds in the presence of mercury acetate leads to thiophenes 80. Mercury complexes 78 derived from 77 react with 1,3-dicarbonyl compounds to generate intermediates 79, which undergo cyclization and subsequent hydrolysis-deacylation to afford 80 <1998JOC6086, 2000JOC3690, 2000JHC363>. Thiophenes 82 <20020L873, 2004JOC4867> are also prepared by reaction of 77 with 2-diazo-3-trimethylsilyloxy-3-butenoate 81 (Scheme 18). 

Conversion of a carbonyl to a gem-dichloro roup is carried out with phosphorus pentachloride [67, 6S] (equations 51 and 52). Under these conditions, 1,4-dicatbonyl compounds give cyclic ethers [67] (equation 53). 

Scheme 5.38 General scheme of disconnection of 1,4-dicatbonyl compounds...

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